1. Field of the Invention
In general, a multi-functional actuator functions to output an electrically or electronically received voice signal or a previously inputted bell or melody as an audible sound, or a vibration signal as a call-incoming signal. Such a function of the multi-functional actuator has been used in mobile communication devices such as a mobile telephone, a pager and so on, however, since the mobile communication devices are required to be carried always or used in a crowded place, the mobile communication devices can be impacted, i.e., dropped or collided into a hard object regardless of the intention of a user so that deformation can be caused to an internal structure thereof.
Therefore, necessity is increasing for a multi-functional actuator with a structure which can withstand such an unexpected impact.
2. Description of the Related Art
A typical multi-functional actuator used in the mobile communication devices has a configuration as shown in FIG. 1, and is comprised of a housing 8 having an internal space and grooves in the inner side; a diaphragm 1 with an outer end fixed to the upper end of the housing 8; a voice coil 2 fixed to the lower end of the diaphragm 8; a vertically magnetized magnet 4; an upper yoke 3 and a lower yoke 5 attached to the magnet 4 for defining a magnetic system together with the magnet; a weight 6 for defining a vibrating body; a plurality of leaf springs 7 and 9 fixed in the grooves of the housing 8; and a vibration-generating coil 10 installed on the grill in the housing 8 for generating vibration by using a magnetic flux formed in the magnetic system.
In this case, if the mutual position and assembled condition of those components are deformed by an external impact or disturbance, the multi-functional actuator cannot perform its own function.
Therefore, components used in a mobile communication terminal such as a mobile telephone and a pager are dropped in various angles and directions as a preliminary test, and the multi-functional actuator also undergoes a test like this.
In this test, a jig is used in order to apply impacts to the multi-functional actuator as an object article of the test from certain heights, and the article is repeatedly dropped for several times with upper, lower and lateral surfaces facing downward. Here, an opposed dropping surface is adopted as a sheet iron which is made of a hard material so as to generally apply an impact to the article.
When article conditions before and after dropping are inspected in such a test, the typical multi-functional actuator of the prior art shows most of the deformation between the housing 8 and the leaf spring 7 when dropped with the side-surface facing downward, which is caused by a rotational moment M generated along the circumferential direction in spiral shape. FIG. 2 shows a rotational moment like this.
FIG. 3 shows a shape of a general leaf spring, which is fixedly supported by the grooves provided in the inner side of the housing. Here, the leaf spring servers to support the weight and determine the natural frequency of a system together with the mass of the weight thereby influencing the generation of sound and vibration according to an input excitation frequency.
In other words, it is required that the values of the mass m and the spring constant k should not be varied, which are important factors in determining the natural frequency of the system.